[llvm] [DomTree] Provide a way to query if DFSInfo is valid (PR #91251)

[via llvm-commits]

hiraditya wrote:

> I don't see why you'd need this; updateDFSNumbers short-circuits if the numbers are already up-to-date.

Let's say i want to use DFSIn number, how do i know DFSIn number is valid calling updateDFSNumbers?

The use case is:
- in the beginning of pass i call updateDFSNumbers
- i use dfsin numbers for ordering
- modify (or not) CFG to split basic blocks
- i want to use dfs in numbers.

One approach would be to keep a boolean (CFGModified for example) in the pass itself. but having this API will simplify it.


https://github.com/llvm/llvm-project/pull/91251